1. Field of the Invention
The present invention relates to a magneto-resistive effect element (MR element), and it particularly relates to an MR element where an antiferromagnetic layer that fixes a magnetization direction of a pinned layer is recessed from the air bearing surface (ABS).
2. Description of the Related Art
A MR element has a multilayer film inducing a magneto-resistive effect, and two magnetic shield layers between which the multilayer film is disposed in the down track direction (track circumferential direction or lamination direction of the multilayer film). For the multilayer film, a spin-valve film is commonly used. The spin-valve film has a free layer where its magnetization direction is changed relative to an external magnetic field, a first pinned layer where its magnetization direction is fixed relative to the external magnetic field, and a spacer layer positioned between the free layer and the first pinned layer. The spacer layer is a nonmagnetic layer that generates a magneto-resistive effect. The multilayer film further has a second pinned layer that fixes the magnetization direction of the first pinned layer and an antiferromagnetic layer that fixes the magnetization of the second pinned layer. The gap between the two magnetic shield layers is referred to as a read gap. In order to enhance the recording density of the magnetic recording medium, particularly the linear recording density, which is the recording density in the down track direction, it is effective to reduce the read gap.
U.S. Pat. No. 7,952,839 discloses an MR element that is provided with an antiferromagnetic layer recessed from the air bearing surface (ABS). The MR element has an inner shield layer positioned between the two magnetic shield layers. The inner shield layer is disposed on the magnetic shield layer adjacent to the antiferromagnetic layer, and faces the ABS. A nonmagnetic conductive layer (cap layer) facing the ABS is disposed between the inner shield layer and the first pinned layer. The antiferromagnetic layer makes contact with the back surface of the inner shield layer viewed from the ABS, but does not face the ABS. The second pinned layer is disposed on the antiferromagnetic layer, and, similar to the antiferromagnetic layer, the second pinned layer does not face the ABS. A portion of the first pinned layer extends to the ABS on the nonmagnetic conductive layer.
U.S. Pat. No. 8,711,528 discloses an MR element where an antiferromagnetic layer is recessed from an ABS. The MR element has an inner shield layer positioned between two magnetic shield layers. The inner shield layer is disposed on the magnetic shield layer adjacent to the antiferromagnetic layer, and faces the ABS. The second pinned layer and the first pinned layer extend to the ABS on the magnetic shield layer.
In these MR elements, because the inner shield layer is disposed on the ABS instead of the antiferromagnetic layer, it is easy to reduce the read gap. Due to this, high-frequency characteristics and bit error rate are also improved. Since the antiferromagnetic layer is away from the ABS, it is difficult a sense current to pass, and the thermostability of the antiferromagnetic layer is improved. Since the antiferromagnetic layer is away from the ABS, corrosion resistance of the antiferromagnetic layer is also improved.
In general, in a spin-valve type MR element, the magnetization direction of the first pinned layer is fixed to a direction orthogonal to the ABS (hereinafter, referred to as the height direction) regardless of the presence of an external magnetic field. A pair of bias layers that apply a bias magnetic field to the free layer are disposed on both sides of the free layer in the cross track direction (the direction orthogonal to the down track direction and the height direction), so as to allow the magnetization direction of the free layer to be oriented in the cross track direction. As a result, the magnetization direction of the free layer is ideally orthogonal to the magnetization direction of the first pinned layer when no external magnetic field exists. When an external magnetic field is applied to the free layer, the magnetization direction of the free layer rotates. The resistance value of the sense current flowing in the multilayer film varies according to the angle of rotation between the magnetization direction of the free layer and that of the first pinned layer. This is referred to as the magneto-resistive effect. Magnetic information recorded in the magnetic recording medium is read based on the magneto-resistive effect of the MR element.
In the MR element described in U.S. Pat. No. 7,952,839, the antiferromagnetic layer makes contact with the inner shield layer, and, in the MR element described in U.S. Pat. No. 8,711,528, the antiferromagnetic layer is electrically connected to the inner shield layer via a conductive seed layer. Consequently, the sense current flowing in the inner shield layer flows in the antiferromagnetic layer. Since the antiferromagnetic layer produces heat by the applied current, the ratio of grains exceeding the blocking temperature (temperature where the bias magnetic field disappears) is increased. A force to fix the magnetization direction of the second pinned layer by the antiferromagnetic layer is weakened, and the magnetization direction of the second pinned layer tends to rotate in the direction of the magnetic field to be applied to the second pinned layer at the moment. As a result, the magnetization direction of the first pinned layer tends to rotate, and is no longer stable in the height direction. A shift of the magnetization direction of the first pinned layer from the height direction causes an increase in noise.
Therefore, the objective of the present invention is to provide a magnetoresistive effect element (MR element) where an antiferromagnetic layer is recessed from the air bearing surface (ABS), and the magnetization direction of the antiferromagnetic layer is stable.